ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus PublicationsGöttingen, Germany10.5194/acp-8-1835-2008Investigating the sources and atmospheric processing of fine particles from Asia and the Northwestern United States measured during INTEX BPeltierR. E.16HecobianA. H.1WeberR. J.1StohlA.2AtlasE. L.3RiemerD. D.3BlakeD. R.4ApelE.5CamposT.5KarlT.51Georgia Institute of Technology, School of Earth and Atmospheric Science, Atlanta, GA 30332-0340, USA2Norwegian Institute for Air Research, 2027 Kjeller, Norway3University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL 33149-1098, USA4Department of Chemistry. University of California Irvine, Irvine, CA, 92697-2025, USA5National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO 80307, USA6now at: Department of Environmental Medicine, NYU School of Medicine, Tuxedo, NY 10987, USA270320088618351853This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from http://www.atmos-chem-phys.net/8/1835/2008/acp-8-1835-2008.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/8/1835/2008/acp-8-1835-2008.pdf

During the National Aeronautics and Space Administration (NASA)
Intercontinental Chemical Transport Experiment, Phase B (INTEX-B), in the
spring of 2006, airborne measurements were made in the United States Pacific
Northwest of the major inorganic ions and the water-soluble organic carbon
(WSOC) of submicron (PM<sub>1.0</sub>) aerosol. An atmospheric trajectory
(HYSPLIT) and a Lagrangian particle dispersion model (Flexpart) quantifying
source contributions for carbon monoxide (CO) were used to segregate air
masses into those of primarily Asian influence (&gt;75% Asian CO) or
North American influence (&gt;75% North American CO). Of the measured
compounds, fine particle mass mostly consisted of water-soluble organic
carbon and sulfate, with median sulfate and WSOC concentrations in two to
four times higher, respectively, in North American air masses versus
transported Asian air masses. The fraction of WSOC to sulfate in transported
Asian air masses was significantly lower than one at altitudes above 3 km
due to depleted organic aerosol, opposite to what has been observed closer
to Asia and in the northeastern United States, where organic components were
at higher concentrations than sulfate in the free troposphere. The
observations could be explained by loss of sulfate and organic aerosol by
precipitation scavenging, with reformation of mainly sulfate during
advection from Asia to North America. In contrast to free tropospheric
measurements, for all air masses below approximately 2 km altitude median
WSOC-sulfate ratios were consistently between one and two. WSOC sources were
investigated by multivariate linear regression analyses of WSOC and volatile
organic compounds (VOCs). In Asian air masses, of the WSOC variability that
could be explained (49%), most was related to fossil fuel combustion
VOCs, compared to North American air masses, where 75% of the WSOC
variability was explained through a nearly equal combination of fossil fuel
combustion and biogenic VOCs. Distinct WSOC plumes encountered during the
experiment were also studied. A plume observed near the California Central
Valley at 0.6 km altitude was related to both fossil fuel combustion and
biogenic VOCs. Another Central Valley plume observed over Nevada at 3 to 5 km,
in a region of cloud detrainment, was mostly related to biogenic VOCs.